Twin Research

Articles

Diagnosing Zygosity in Infant Twins: Physical Similarity, Genotyping, and Chorionicity

Nadine Forget-Duboisa1, Daniel Pérussea2 c1, Gustavo Tureckia3, Alain Girarda4, Jean-Michel Billettea5, Guy Rouleaua6, Michel Boivina7, Jocelyn Maloa8 and Richard E. Tremblaya9

a1 Research Unit on Children's Psychosocial Maladjustment, University of Montreal, Montreal, Canada.

a2 Research Unit on Children's Psychosocial Maladjustment, University of Montreal, Montreal, Canada. Daniel.Perusse@umontreal.ca

a3 Douglas Hospital Research Center, McGill University, Montreal, Canada.

a4 Research Unit on Children's Psychosocial Maladjustment, University of Montreal, Montreal, Canada.

a5 Research Unit on Children's Psychosocial Maladjustment, University of Montreal, Montreal, Canada.

a6 Douglas Hospital Research Center, McGill University, Montreal, Canada.

a7 Research Unit on Children's Psychosocial Maladjustment, Laval University, Quebec City, Canada.

a8 Research Unit on Children's Psychosocial Maladjustment, University of Montreal, Montreal, Canada.

a9 Research Unit on Children's Psychosocial Maladjustment, University of Montreal, Montreal, Canada.

Abstract

We compared the results of different methods for diagnosing zygosity in a sample of 237 same-sex pairs of twins assessed at 5 and 18 months of age. Despite the twins' very young age and early stage of development, physical similarity was concordant with genotyping in 91.9% of cases at 5 months and 93.8% of cases at 18 months, for a subsample of 123 and 113 pairs, respectively. This concordance rate was obtained following a case-by-case assessment of each pair's physical similarity using a shortened version of the Zygosity Questionnaire for Young Twins (Goldsmith, 1991). Taking into account the chorionicity data available from the twins' medical files, we were able to classify correctly 96% of the pairs, an accuracy rate comparable to previously reported rates obtained with older twins. Chorionicity data is especially useful since we found that monochorionic MZ twins are more difficult than dichorionic MZ twins to diagnose by physical similarity at these young ages. The relative cost-benefit of methods based on reported physical similarity and DNA analysis is discussed in light of these results.

Correspondence:

c1 Address for correspondence: Daniel Pérusse, Research Unit on Children's Psychosocial Maladjustment-University of Montreal, Ste-Justine Hospital Research Center, Bio-psychosocial Unit, Block 5, floor A, 3175, Chemin de la Côte Ste-Catherine, Montreal, Canada, H3T 1C5.

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